1. Field of the Invention
The present invention relates to refrigeration and freezing. More particularly, it relates to an ambient air freezing system and process capable of chilling ambient air to cryogenic temperatures of -120.degree. C. without the use of cryogenic chemicals or other refrigerants.
2. The Prior Art
Refrigeration is a process of cooling or freezing a substance to a temperature lower than that of its surroundings and maintaining that substance in a cold state. Refrigeration can be performed by conventional methods such as convection or thermal conduction. Other, more complex methods include the exploitation of thermoelectric properties of semiconductors, the magnetothermoelectric effects in semimetals, or the diffusion of .sup.3 He atoms across the interface between distinct phases of liquid helium having high and low concentrations of .sup.3 He in .sup.4 He.
Commercial refrigeration systems such as, for example, a vapor-compression refrigerator use refrigerants to obtain the low temperatures within the desired area. This type of refrigerator consists of a compressor, a condenser, a storage tank, a throttling valve and an evaporator. The refrigerant is a liquid which partly vaporizes and cools as is passes through the throttling valve. Among the common refrigerants are ammonia, sulfur dioxide, and various halides of methane and ethane. The most commonly used are the Freons.RTM. of which Freon-12.RTM. is dichlorodifluoromethane. In the vapor-compression system, near constant pressures are maintained on either side of the throttling valve by the compressor.
Another example of a refrigeration system of the prior art is a vapor-absorption refrigeration system. In this system, there are no moving parts. The added energy comes from a gas or liquid fuel burner or from an electrical heater, as heat, rather than from the compressor, as work. This system also uses a refrigerant while maintaining total pressure throughout the system is constant and therefore no valves are needed.
With the growing awareness of the environmental effects of using refrigerants to obtain low refrigeration temperatures, it is desirable to have a refrigeration system that utilizes nothing but ambient air and does not use refrigerants to produce refrigeration temperatures down into the cryogenic range.